1. Field of the Invention
This invention relates to drying solid particles and, more particularly, to an apparatus and method for drying solid particles such as fertilizers.
2. Description of Related Art
The manufacture of fertilizers is generally carried out by agglomeration or prilling processes in which particles such as prills or granules of the fertilizer are formed. There are numerous agglomeration and prilling processes known for the manufacture of fertilizers such as ammonium nitrate, urea, potash and phosphates. Agglomeration processes are generally carried out in paddle mixers, pug mills, rotary drums, pans or fluidized beds. Prilling processes are usually carried out in prilling vessels such as prilling towers.
In many cases the fertilizer particles formed in these processes must be dried. Traditional moving bed dryers typically rely upon a large volume of air to purge the solids bed and remove water.
However, traditional moving bed dryers have high capital and operating costs associated with air scrubbing requirements. In addition, conventional moving bed dryers are frequently complex in operation.
U.S. Pat. No. 5,167,274 discloses a method and apparatus for cooling particulate solids. This patent teaches that free-flowing solid particles are cooled in an apparatus comprising a housing containing a multiplicity of parallel, vertical, expanded heat exchanger plates having a cooling fluid therein. However, U.S. Pat. No. 5,167,274 does not disclose the drying of solid particles.
U.S. Pat. No. 3,181,488 discloses a coal drying apparatus that includes vertical hollow plates containing a heated liquid. Air chambers positioned beneath the plates discharge atmospheric air upwardly through coal particles passing between the plates to carry off water vapor. However, U.S. Pat. No. 3,181,488 does not disclose the use of dehumidified gas to dry coal particles.
There is a need for an improved moving bed dryer having reduced air scrubbing requirements, lower operating costs, reduced capital costs and simplicity of operation in drying solid particles.